1. Field of the Invention
The present invention generally relates to a common rail such as a high pressure fuel manifold in an accumulator fuel injection system of a diesel engine or a block rail.
2. Description of the Prior Arts
Conventionally, as thick kind of common rail, for example, as shown in FIG. 11, there has been known a common rail of the type which is structured such that a branch hole 21-2 portion communicating with an inner communication passage 21-1 disposed in a peripheral wall portion of a main pipe rail 21 end constituted by a circular pipe is made a pressure receiving seat surface 21-3 open to an outer direction, and pressing seat surface 22-3 constituted by a connection head portion 22-2 of a branch pipe 22 having a tapering conical shape and enlarged a diameter thereof by buckling is brought into contact and engaged with an end portion by using a joint metal fitting 23 surrounding an outer peripheral portion of the main pipe rail 21 adjacent to the pressure receiving seat surface, thereby fastening and connecting to a screw wall 23-1 portion projecting to the joint metal fitting 23 together with pressing under the connection head portion 22-2 neck by means of an engagement of a fastening nut 24 previously assembled in the branch pipe end. In the drawing, reference numeral 22-1 denotes a flow passage of the branch pipe 22 and reference numeral 25 denotes a sleeve washer.
However, in the case of the common rail of the type that the joint metal fitting type common rail which is structured such that the joint metal fitting 23 is outwardly fitted to the main pipe rail 21 and the nut 24 meshed with the joint metal fitting 23 is fastened and connected, as shown in FIG. 11, a great stress is generated in an inner peripheral edge portion P of a lower end of the branch hole 12-2 due to an axial force applied to the pressure receiving seat surface 21-3 together with the internal pressure of the main pipe rail 21 and the pressing of the connection head portion 22-2 in the branch pipe 22, so that a crack is easily generated with starting from the lower end inner peripheral edge portion P and there is a possibility of inviting a leakage.
The present invention is made so as to solve the conventional problems mentioned above, and an object of the invention is to provide a common rail which can reduce a maximum tensile stress value generated in an inner peripheral edge portion of a lower end of a branch hole and can improve an internal pressure fatigue strength and a method of manufacturing the same.
In order to achieve the object mentioned above, in accordance with a first aspect of the invention, there is provided a common rail comprising at least one branch hole provided in an axial peripheral wall portion of a main pipe rail having a communication passage inside an axial core, a pressure receiving seat surface communicating with a branch pipe having a communication passage communicating with the communication passage in a peripheral surface portion of the branch hole and open to an outer portion, thereby bringing a pressing seat surface portion constituted by a connection head portion disposed in an end portion of the branch pipe into contact and engaging therewith, and a joint metal fitting surrounding an outer peripheral portion of the main pipe rail and a nut previously assembled in the branch pipe end which are meshed with each other so as to be pressed under a neck portion of the connection head portion, thereby being fastened and connected, in which a compression residual stress is present at a portion near the open end portion of the communication passage of the main pipe rail in the branch hole.
Further, in accordance with a second aspect of the invention, there is provided a method of manufacturing a common rail comprising at least one branch hole provided in an axial peripheral wall portion of a main pipe rail having a communication passage inside an axial core, a pressure receiving seat surface communicating with a branch pipe having a communication passage communicating with the communication passage in a peripheral surface portion of the branch hole and open to an outer portion, thereby bringing a pressing seat surface portion constituted by a connection head portion disposed in an end portion of the branch pipe into contact and engaging therewith, and a joint metal fitting surrounding an outer peripheral portion of the main pipe rail and a nut previously assembled in the branch pipe end which are meshed with each other so as to be pressed under a neck portion of the connection head portion, thereby being fastened and connected, in which a pressing force is applied to the main pipe rail near the branch hole from an outer portion to a diametrical direction, preferably by a press method, thereby generating a compression residual stress at a portion near the open end portion of the communication passage of the main pipe rail in the branch hole. Further, in this case, the branch hole is punched at the same time as the pressing force is applied to the main pipe rail near the branch hole form the outer portion to the diametrical direction by an external pressing method.
Still further, in accordance with a third aspect of the invention, there is provided a method of manufacturing a common rail comprising at least one branch hole provided in an axial peripheral wall portion of a main pipe rail having a communication passage inside an axial core, a pressure receiving seat surface communicating with a branch pipe having a communication passage communicating with the communication passage in a peripheral surface portion of the branch hole and open to an outer portion, thereby bringing a pressing seat surface portion constituted by a connection head portion disposed in an end portion of the branch pipe into contact and engaging therewith, and a joint metal fitting surrounding an outer peripheral portion of the main pipe rail and a nut previously assembled in the branch pipe end which are meshed with each other so as to be pressed under a neck portion of the connection head portion, thereby being fastened and connected, in which a pressing force is applied to an inner peripheral surface of the main pipe rail near the branch hole by an internal pressing method, thereby generating a compression residual stress at a portion near the open end portion of the communication passage of the main pipe rail in the branch hole.
Furthermore, in accordance with a fourth aspect of the invention, there is provided a method of manufacturing a common rail comprising at least one branch hole provided in an axial peripheral wall portion of a main pipe rail having a communication passage inside an axial core, a pressure receiving seat surface communicating with a branch pipe having a communication passage communicating with the communication passage in a peripheral surface portion of the branch hole and open to an outer portion, thereby bringing a pressing seat surface portion constituted by a connection head portion disposed in an end portion of the branch pipe into contact and engaging therewith, and a joint metal fitting surrounding an outer peripheral portion of the main pipe rail and a nut previously assembled in the branch pipe end which are meshed with each other so as to be pressed under a neck portion of the connection head portion, thereby being fastened and connected, in which a pressing force is applied to an inner peripheral surface of the main pipe rail near the branch hole by a pipe expansion method which applies a pressure to a pipe diametrical direction from an inner portion of the main pipe rail, thereby generating a compression residual stress at a portion near the open end portion of the communication passage of the main pipe rail in the branch hole.
Moreover, in accordance with a fifth aspect of the invention, there is provided a method of manufacturing a common rail comprising at least one branch hole provided in an axial peripheral wall portion of a main pipe rail having a communication passage inside an axial core, a pressure receiving seat surface communicating with a branch pipe having a communication passage communicating with the communication passage in a peripheral surface portion of the branch hole and open to an outer portion, thereby bringing a pressing seat surface portion constituted by a connection head portion disposed in an end portion of the branch pipe into contact and engaging therewith, and a joint metal fitting surrounding an outer peripheral portion of the main pipe rail and a nut previously assembled in the branch pipe end which are meshed with each other so as to be pressed under a neck portion of the connection head portion, thereby being fastened and connected, in which after a pressing force is applied to an inner peripheral surface of the main pipe rail, the branch hole is punched.
Further, in accordance with a sixth aspect of the invention, there is provided a method of manufacturing a common rail comprising at least one branch hole provided in an axial peripheral wall portion of a main pipe rail having a communication passage inside an axial core, a pressure receiving seat surface communicating with a branch pipe having a communication passage communicating with the communication passage in a peripheral surface portion of the branch hole and open to an outer portion, thereby bringing a pressing seat surface portion constituted by a connection head portion disposed in an end portion of the branch pipe into contact and engaging therewith, and a joint metal fitting surrounding an outer peripheral portion of the main pipe rail and a nut previously assembled in the branch pipe end which are meshed with each other so as to be pressed under a neck portion of the connection head portion, thereby being fastened and connected, in which a pressing force is applied to an inner peripheral surface of the branch hole by a diameter expansion method which applies a pressure to a pipe diametrical direction from an inner portion of the branch hole, thereby generating a compression residual stress at a portion near the open end portion of the communication passage of the main pipe rail in the branch hole.
Still further, in accordance with a seventh aspect of the invention, there is provided a method of manufacturing a common rail comprising at least one branch hole provided in an axial peripheral wall portion of a main pipe rail having a communication passage inside an axial core, a pressure receiving seat surface communicating with a branch pipe having a communication passage communicating with the communication passage in a peripheral surface portion of the branch hole and open to an outer portion, thereby bringing a pressing seat surface portion constituted by a connection head portion disposed in an end portion of the branch pipe into contact and engaging therewith, and a joint metal fitting surrounding an outer peripheral portion of the main pipe rail and a nut previously assembled in the branch pipe end which are meshed with each other so as to be pressed under a neck portion of the connection head portion, thereby being fastened and connected, in which a piece-like body formed in a spherical body or having a tapered front end is pressed to an open end portion of the communication passage of the main pipe rail of the branch hole, thereby generating a compression residual stress at a portion near the open end portion of the communication passage of the main pipe rail in the branch hole.
Accordingly, in accordance with the invention, by remaining a compression residual stress at a portion near the open end portion of the communication passage of the main pipe rail in the branch hole, a tensile stress generated in an inner peripheral edge portion P of the lower end of the branch hole by an axial force applied to the pressure receiving seat surface together with an internal pressure of the main pipe rail and a pressing by the connection head portion of the branch pipe is canceled by the compression residual stress, thereby reducing a maximum tensile stress value generated in the inner peripheral edge portion of the lower end of the branch hole. As a method of generating and remaining a compression residual stress at a portion near the open end portion of the communication passage of the main pipe rail in the branch hole, the following methods are used, (1) a method of applying a pressing force to the main pipe rail from an outer portion in a diametrical direction by a press method, (2) a method of applying a pressure within the communication passage of the main pipe rail, (3) a pipe expansion method of applying a pressure from the inner portion of the main pipe rail in a pipe expanding direction, (4) a diameter expansion method of applying a pressure from the inner portion of the branch hole in a diametrical direction, and (5) a method of pressing a piece-like body formed in a spherical body or having a tapered front end to the open end portion of the communication passage of the main pipe rail in the branch hole.
In this case, the press method for generating a compression residual stress at a portion near the open end portion of the communication passage of the main pipe rail in the branch hole is performed before or after or at the same time of punching the branch hole, the communication passage internal pressure pipe expansion method may be performed before or after punching the branch hole, however, is preferably performed after punching the branch hole, and the branch hole diameter expansion method is performed after punching the branch hole.
In accordance with the invention, as (1) the method of applying a pressing force from the outer portion of the main pipe rail by a press method, for example, a method of pressing by a punch or a rod in a state of mounting the rail body on a female mold having a circular arc groove and pressing and fixing by right and left movable molds can be used.
Further, as (2) the method of applying a pressure within the communication passage of the main pipe rail, it is preferable to use a hydraulic pressure such as an oil pressure or a water pressure.
Next, as (3) the pipe expansion method of applying a pressing force from the inner portion of the main pipe rail to the pipe diametrical direction, for example, a method of pressure welding by a drawing-out method of a pressing method by means of a diameter expansion device such as a spherical body or a shell-like plug having a diameter slightly larger than an inner diameter of the communication passage within the communication passage of the main pipe rail, or a diameter expansion method by a vanishing tool can be used.
Further, as (4) the method of applying a pressure from the inner portion of the branch hole to a diametrical direction, a method of pressure welding a spherical body or a plug having a diameter slightly larger than an inner diameter of the branch hole by a pressing method can be used.
Still further, as (5) the method of pressing a piece-like body formed in a spherical body or having a tapered front end to the open end portion of the communication passage of the main pipe rail in the branch hole, with using a piece-like body formed in a spherical body or having a front end formed in a tapered conical shape, an oval conical shape or an oblong conical shape, for example, a method of inserting a rigid ball and a rigid ball receiver or a piece-like body having a tapered front end and a piece-like body receiver into the main pipe rail, arranging the rigid ball receiver or the piece-like receiver in such a manner that the spherical surface of the rigid ball or the front conical surface of the piece-like body is brought into contact with the open end portion of the communication passage of the main pipe rail in the branch hole, inserting and pressing a punch having a wedge-like front end from the other end portion of the main pipe rail and pressing the spherical surface of the rigid ball or the front end conical surface of the piece-like body to the open end portion of the communication passage of the main pipe rail in the branch hole can be used.
As mentioned above, in accordance with the invention, by remaining a compression residual stress at the portion near the open end portion of the communication passage of the main pipe rail in the branch hole, the tensile stress generated in the inner peripheral edge portion of the lower end of the branch hole at a time of a high pressure fuel accumulation to the communication passage in a use time can be canceled by a compression residual stress so as to be effectively restricted, thereby improving an internal pressure fatigue strength in the branch pipe connecting portion.